1. Field of the Invention
The present invention relates to a hard disk drive, and more particularly, to hard disk drive having a disk fluttering reducing unit which reduces fluttering of a rotating disk.
2. Description of the Related Art
A hard disk drive (HDD) is one of auxiliary memory devices of a computer, which reads out data stored in a magnetic disk or records data on the magnetic disk by using a magnetic head. Recently, a variety of research and development efforts are being performed to realize the hard disk drive having a high speed, a high capacity, low fluttering, and a low noise.
FIG. 1 is a plan view showing a conventional hard disk drive, and FIG. 2 is an enlarged perspective view of a portion of the hard disk drive of FIG. 1.
Referring to FIGS. 1 and 2, the hard disk drive includes a magnetic disk (a hard disk) 20 which is a recording medium storing of data, a spindle motor 30 installed on a base 10 to rotate the disk 20, and an actuator 40 having a magnetic head 41 to reproduce the data recorded in the disk 20.
As the disk 20, a single disk or a plurality of disks are installed to be rotated by the spindle motor 30 and separated by a predetermined distance from each other. A parking zone 21 where a slider 42 is located when power of the hard disk drive is off is provided at an inner circumferential side of the disk 20, and a data zone 22 where a magnetic signal is recorded is provided outside the parking zone 21. A servo signal indicating a position of information to be recorded is recorded on several tens of thousands of tracks formed along a circumference of the disk 20.
The actuator 40 is installed to be capable of pivoting by a voice coil motor 48 around a pivot shaft 47 installed on the base 10. The actuator 40 includes an arm 46 coupled to the pivot shaft 47 to be capable of pivoting, and a suspension 44 which supports a slider 42 installed at the arm 46 to be elastically biased toward a surface of the disk 20. The magnetic head 41 is mounted on the slider 42.
When the power of the hard disk drive is off, the slider 42 is disposed in the parking zone 21 of the disk 20 by an elastic force of the suspension 44. When the power is turned on, and the disk 20 starts to rotate, a lift force is generated by air pressure, and accordingly the slider 42 is lifted. The slider 42 being lifted is moved to the data zone 22 of the disk 20 as the actuator 40 pivots. The slider 42 moved to the data zone 22 of the disk 20 maintains a lifted state at a height where the lift force by a rotation of the disk 20 and the elastic force by the suspension 44 are balanced, as shown in FIG. 3. Thus, the magnetic head 41 mounted on the slider 42 records and reproduces data on and from the disk 20 as it maintains a predetermined distance from the disk 20 that is rotating.
However, in the conventional hard disk drive having the above structure, fluttering of the disk 20 is caused by defective parts of the spindle motor 30, eccentricity in an assembly of the disk 20, or an irregular air flow occurring during the rotation of the disk 20 in the hard disk drive. As the fluttering, there is RRO (repeatable runout) that is a component repeated at each of rotations and NRRO (non-repeatable runout) that is a component which is not repeated. The RRO which regularly repeats can be compensated by a servo control system to a certain degree whereas the NRRO is difficult to be anticipated and compensated. The disk fluttering reduces a data recording and reproduction capability of the magnetic head 41 and finally exerts a bad influence on a performance of the hard disk drive.
Conventionally, when the disk fluttering is generated at the disk 20, an interval between the slider 42 and the disk 20 can be maintained to a certain degree by a damping effect by air existing therebetween. However, as a rotation speed of the disk 20 increases, and a thickness of the disk 20 decreases, the disk fluttering is amplified so that accurate recording or reproduction of data is made difficult by only a servo control system and an air damping effect between the slider 42 and the disk 20. Further, as TPI (track per inch) increases recently, the disk fluttering makes an accurate control of a position of the magnetic head 41 difficult.
In light of the above, it is necessary to reduce the disk fluttering occurring during an operation to secure reliability in the performance of the hard disk drive. Furthermore, as the hard disk drive recently exhibits a high speed, a high capacity, and a low noise, it is important to reduce disk fluttering.